1. Field of Invention
The present invention relates to a display panel. More particularly, the present invention relates to an optical interference display panel.
2. Description of Related Art
Due to being lightweight and small in size, a display panel is favorable in the market of portable displays and displays with space limitations. To date, in addition to liquid crystal display (LCD), organic light emitting diode (OLED) and plasma display panel (PDP) modules, a module of the optical interference display has been investigated.
U.S. Pat. No. 5,835,255 discloses a modulator array, that is, a color-changeable pixel for visible light which can be used in a display panel. FIG. 1A illustrates a cross-sectional view of a prior art modulator. Every modulator 100 comprises two walls, 102 and 104. These two walls are supported by posts 106, thus forming a cavity 108. The distance between these two walls, the depth of cavity 108, is D. The wall 102 is a light-incident electrode which, according to an absorption factor, absorbs visible light partially. The wall 104 is a light-reflection electrode that is flexed when a voltage is applied to it.
When the incident light shines through the wall 102 and arrives at the cavity 108, only the visible light with wavelengths corresponding to the formula 1.1 is reflected back, that is,2D=Nλ  (1.1)
wherein N is a natural number.
When the depth of the cavity 108, D, equals one certain wavelength λ1 of the incident light multiplied by any natural number, N, a constructive interference is produced, and a light with the wavelength λ1 is reflected back. Thus, an observer viewing the panel from the direction of the incident light will observe light with the certain wavelength λ1 reflected back at him. The modulator 100 here is in an “open” state.
FIG. 1B illustrates a cross-sectional view of the modulator 100 in FIG. 1A after a voltage is applied to it. Under the applied voltage, the wall 104 is flexed by electrostatic attraction toward the wall 102. At this moment, the distance between the walls 102 and 104, the depth of cavity 108, becomes d and may equal zero.
The D in the formula 1.1 is hence replaced with d, and only the visible light with another certain wavelength λ2 satisfying the formula 1.1 produces a constructive interference and reflects back through the wall 102. However, in the modulator 100, the wall 102 is designed to have a high absorption rate for the light with the wavelength λ2. Thus, the incident visible light with the wavelength λ2 is absorbed, and the light with other wavelengths has destructive interference. All light is thereby filtered, and the observer is unable to see any reflected visible light when the wall 104 is flexed. The modulator 100 is now in a “closed” state, i.e. a dark state.
As described above, under the applied voltage, the wall 104 is flexed by electrostatic attraction toward the wall 102, such that the modulator 100 is switched from the “open” state to the “closed” state. When the modulator 100 is switched from the “closed” state to the “open” state, the voltage for flexing the wall 104 is removed, and the wall 104 elastically returns to the original state, i.e. the “open” state or light state, as illustrated in FIG. 1A.
The light-reflection electrode (the wall 104) is a membrane, typically made of metal, and generally is manufactured with a “sacrificial layer” technique widely used in the production of micro electro mechanical systems (MEMS). The light-reflection electrode is very thin and is easily damaged by even a tiny external force or by errors occurring during manufacturing, inhibiting it from functioning properly.
For example, the light-reflection electrode may receive defects by being touched during manufacturing or transporting procedures. A color-changeable pixel containing defects is unable to reflect the incident light at defect locations. Moreover, an observer is able to look through the defects at things behind the optical interference display panel, such as circuit boards or even light from another light source.
When the color-changeable pixel containing defects is operated in the dark state, the light from another light source behind it may pass through the defects and be emitted outward so as to make the color-changeable pixel act in an undesired “light” state. Furthermore, after passing through the defects, the original incident light is reflected by the things behind the color-changeable pixel, such as metal lines on the circuit board. The reflected light is directly emitted outward without being filtered by the color-changeable pixel, thus causing another undesired appearance of a “light” state. These undesired “light” states of the color-changeable pixel resemble bad pixels on the optical interference display panel.
Display panel contrast is typically defined as a ratio of the brightness of the “light” state to the “dark” state. The optical interference display panel totally comprises a plurality of color-changeable pixels. Therefore, the color-changeable pixels having defects which cause bad pixels lower the contrast and the display performance of the display panel.